WASHINGTON — The Pentagon is considering ways to bring the Sunni Arab tribes of Iraq's Anbar province more fully into the battle against the Islamic State group, the top U.S. military officer said Thursday.

Gen. Martin Dempsey, chairman of the Joint Chiefs of Staff, told reporters that expanding U.S. train-and-advise efforts to include the tribes is one of three key elements of a strategy designed to roll back IS fighters in northern and western Iraq.

The other elements are advising and assisting Iraqi government troops and creating so-called national guard units as a sort of quasi-military force that must first gain legal approval from the Iraqi government.

"You need all three of those eventually," Dempsey said. However, a condition for training and advising the tribes would be the willingness of the Iraqi government to arm them, he said.

Speaking alongside Dempsey, Defense Secretary Chuck Hagel agreed that the tribes are an important component of the strategy.

"The Sunni tribes are going to have to be part of this," Hagel said.

Enlisting the help of Anbar's tribes was critical to the success of U.S. efforts to stabilize Iraq in the latter stages of the Iraq war in 2007-2008. Since that period, the tribal leaders have grown disillusioned with the Shiite-dominated government in Baghdad, although Washington has staked its hopes on a more inclusive approach to the Sunnis and Kurds by new Prime Minister Haidar al-Abadi.

Dempsey said the U.S. strategy's first focus is on Iraqi government and Kurdish regional fighters. But the tribes could be an important complement to those.

"That's what we're now beginning to explore," he said. "We've got a program in place where we're beginning to restore some offensive capability and mindset to the Iraqi security forces. We need to think about how to do that with the tribes."

Asked about progress in the administration's project to train members of the Free Syrian Army as a moderate opposition force, Dempsey said the process of recruiting and vetting candidate fighters has not yet begun.

Some have questioned the viability of that project, for which Congress has approved spending $500 million to train up to 5,000 fighters.

President Barack Obama's special envoy for the coalition opposing the Islamic State group, retired Marine Gen. John Allen, said in an interview Wednesday that U.S. support for the Free Syrian Army will ultimately achieve a "political outcome" in Damascus that "does not include" Syrian President Bashar Assad.

Allen told the Al Arabiya Arabic news channel that the goal is to build the Free Syrian Army into a force with "battlefield credibility" to "deal with" IS and to defend itself again Assad regime forces, according to a State Department transcript of the interview.

The Free Syriana Army is a loose coalition of rebels groups fighting to topple Assad. The group's political leadership is based in Turkey, where fighters often seek respite from the fighting. There are various factions within the group whose ideologies are constantly shifting, but generally range from mainstream moderates to deeply conservative Muslims.